Remove __libc_pselect alias.

Continuing the removal of unused __libc_* function names, this patch
removes the __libc_pselect alias.

Tested for x86_64 that installed stripped shared libraries are
unchanged by this patch.

	* misc/pselect.c [!__pselect] (__libc_pselect): Remove alias.
	* sysdeps/unix/sysv/linux/pselect.c [__NR_pselect6]
	(__libc_pselect): Likewise.